FR2627380A1 - Two-part joint prosthesis - has biocompatible flexible tubular shank which wedges in bone medullary channel - Google Patents

Abstract

The joint prosthesis e.g. for a hip, elbow or knee, consists of a shank (4) which fits into the medullary channel of a bone such as the femur and is equipped with a head (2) connected to the joint pivot. The shank is made with a degree of flexibility so that it fits tightly inside the medullary channel, with the flexibility provided by a lengthwise slit (4f) along a shank which is basically tubular in shape. The elasticity can also be provided by using a biocompatible material which forms a wedge fit with the medullary channel. In another variant, the shank can be of slightly smaller dimensions than the channel, and fixed in place by an expander in the shape of a polygonal wedge. The shank can be further held in place with the aid of a clip, staple or other fixing, and it may be made from a biocompatible material with a shape memory, which expands to fit in the channel by virtue of the tissue temp. The shank can have surface projections, grooves or slots to promote osteogenesis. ADVANTAGE - Reduced weight and improved fitting.

Description

The invention relates to an anchoring rod in a medullary canal, in particular for various prostheses of articulation
The subject of the invention is related to the technical sector of implants and prostheses in general
In reconstructive surgery, prostheses are used in which direct linkage components to replace the natural joint are directly connected to or attached to stems or tails, which must be introduced into the medullary canals of the femur and tibia. , then firmly and durably anchored in said channels,
For this purpose, solid, solid and therefore rigid or isoelastic, fasciculated stems have been used up to now, which are shaped in length and in section to correspond to the medullary canal prepared for this purpose. These rods are held in place either by a suitable cement or by special arrangements of the rod (slots, no screws, aspérites, surface condition, flexible branches or strands ...).

Considering that the elements constituting the artificial artificial replacement represent a significant increase in weight relative to the natural organs, it seemed worthwhile to limit this overload as much as possible without impairing the good behavior of the prosthesis.
On the other hand, it is important that the anchor rod is as narrow as possible in section in order to limit the digging of the medullary canal and to maintain a suitable thickness of the implantation zone It is also wise to allow some Flexibility of the stem to get as close as possible to the natural flexing characteristics of the lower limb bone during movements
It is for all these and other reasons that a generally tubular prosthesis stem has been designed from its upper end for connection to the hinge support to its lower free end. rod being made of a biocompatible material preferably having good elasticity characteristics.

 Another problem to be solved is the distribution of the contact pressures with the medullary canal and the good occupation of the medullary canal, which are not completely possible for the stems currently known.

 For this purpose, and according to another characteristic, the tubular rod has from one side a longitudinal slot of elasticity along its entire length.

 Still for this purpose, to facilitate its introduction into the medullary canal, the tubular shaft slotted longitudinally is established with external dimensions in section allowing its free introduction into the medullary canal, then its radial expansion by an independent spacer means, within the limits of the elastic deformation of the material.

 In a reverse manner, the longitudinally slotted tubular rod is established with outside dimensions in section slightly larger than those of the medullary canal for entry force introduced therein or internally forms of cooperation with independent retaining members in the narrowed position of the stem. before implantation, within the limit of its elastic diformation.

 According to another characteristic applied to a rod of tubular shape, the radial expansion of the rod is obtained by the use of a biocompatible material having the shape memory phenomenon.

 Another advantage of making a tubular stem split or not appears in the possibility by the current means of production, to establish outer forms in sections as close as possible to the inner form of the medullary canal, and the corresponding inner forms or evolutive .

 The use of tubular rod still allows good anchoring and bone regrowth through the use of filler materials initiating rehabilitation such as calcium phosphates or other promoting osteogenesis.

 For this, according to another feature, the tubular wall of the rod has on all or part of its surface multiple or various openings or openings through which said material can come into contact with the bone tissue.

 These and other features will become apparent from the following description.

 To fix the object of the invention, without limiting it, there is illustrated a femoral hip prosthesis stem being understood that the invention also applies to the stems or tails of the knee, shoulder, elbow prostheses. ...

 - Figure 1 is an external view showing an unslotted tubular shaft.

 - Figure 2 is a longitudinal sectional view illustrating a slotted tubular shaft.

 FIG. 3 is a plan view corresponding to FIG. 2.

 FIGS. 4, 5 and 6 are cross-sectional views taken respectively along the lines 4-4, 5-5 and 6-6 of FIG. 2.

 FIG. 7 is a partial perspective view illustrating various openings for the passage of wound material and elastic slits.

 - Figure 8 is a partial perspective view of a slotted tubular shaft and threaded externally.

 - Figures 9 and 10 are cross-sectional views illustrating two embodiments of the radial expansion by an independent spacer member.

 FIG. 11 is a cross-sectional view showing an exemplary embodiment of the radial expansion before removal of a retaining member in a narrowed position.

FIGS. 12, 13 and 14 are cross-sectional views illustrating various forms of hollow tubular rods
The femoral stem (F) illustrated is made of a biocompatible material preferably having good elasticity characteristics.

It has in known manner at its upper part and in an oblique plane (1) a neck (2) of connection with the joint
The actual stem (4) attached to the neck has a generally tubular shape whose outer section can between any curved profile or sides, as illustrated in the different figures, and which is preferably degressive from top to bottom, that is, with a flared top zOne (4a) for connection with the cervix, then a slightly conical medial and inferior zone (4b) for engagement in the corresponding medullary canal. It is not excluded that the form has a constant section.

 According to another important feature, the rod (4) is traversed from one side, from its upper face (4c) contiguous to the neck up to its free lower face (4d) by a longitudinal orifice (4e) which is sized to give the rod over most of its length a tubular character with a reduced wall thickness, and preferably flared or not towards the upper part.

 As illustrated in the figures of the drawings, the inner section of the tubular shaft may be of any shape preferably corresponding to the outer shape, but not limited to. On the other hand, as can be seen in FIGS. 4, 5 and 6, the inner and / or outer section shapes can be varied all along the length, by electrospray process with software. appropriate, or other method, to obtain an optimum strength-flexibility ratio, by marrying the inner profile of the medullary canal in the lower or distal portion, with a certain flexural capacity, and in the upper or proximal part, to maintain a more rigid zone and less deforinable to cash the efforts transmitted by the joint.

 According to another important characteristic, in order to obtain an excellent distribution of the contact pressures in the medullary canal, and self-locking with a good occupation of its surface, and to facilitate the implantation of the stem, a longitudinal slot is provided. elasticity (4f) crossing the stem over the entire length. This slot is made at a point diametrically opposed to the neck, without however excluding other directions. This slot may other possibly be limited in length.

 Starting from this notion of slotted tubular stem, various solutions have been provided for easy implantation into the medullary canal. In the first place, this implantation can be carried out by simple forced fitting into the medullary canal.

 According to another solution and as illustrated in Figures 9 and 10, the rod may be of external dimensions in section slightly smaller than those of the medullary canal in order to introduce it freely. Anchoring in said channel with contact pressure is then obtained by forced engagement in the rod of an independent spacer means.

 For example and without limitation, a nail, a wedge, a key, a pin (5) preferably of polygonal section and wedge effect is forced into the opening (4e). Or a similar member (6) is forcibly engaged between two grooves (4g) formed on each side of the longitudinal slot (4f); these organs remaining in position after assembly.

According to another solution illustrated in FIG. 11, in opposite maneuver the rod is of slightly larger cross-sectional shape than that of the medullary canal, and a narrowing is carried out before mounting for sliding insertion; this necking being maintained by any means such as clip (7>, clip, clamp cooperating with projecting shapes (4h) made internally on either side of the longitudinal slot
Of course, these deformations are carried out in the link of the elastic capacity. In order to allow a radial expansion differentiated by zOne in the length, other elasticity slots limited in height are also provided.
I see it in Figure 7, transverse slots (4i) opening in the longitudinal slot. It is thus possible in combination with the shape to closely follow the irregularities of the medullary canal and obtain different deformations by zones.

 According to another interesting feature, the tubular rod may be made of a biocompatible material having the known phenomenon of shape memory, slidingly introduce the rod into the medullary canal, and then obtaining self-locking by radial expansion of the rod. under the increase of the temperature which modifies the shape and / or the dimensions of the stem.

 Note that in this embodiment, the rod is not split longitudinally.

 The realization of a tubular shaft split or not also increases the possibilities of anchoring and bone regrowth. Indeed, it is possible to introduce in the longidutinal opening (4th) a filling material initiating rehabilitation, such as calcium phosphates or other promoting osteogenesis. These products are then brought into contact with the medullary canal by multiple and varied orifices or openings (4j) made on. all or part of the surface of the rod, as shown in Figure 7.

 As seen above, the tubular stem may be of any shape in an outer section, for example circular (FIG. 8), ovoid FIGS. 9, 10, 11X, triangular or trapezoidal (FIG. 12), buttonhole FIG. 13) , elliptical (Figure 14), trefoil Figure 6) or other form. Preferably, in order to evenly distribute the pressures, the inner section of the rod is of corresponding shape, but can also change gradually in length as illustrated in FIGS. 4, 5 and 6, in particular for stretching compatible with the attachment part of the neck while closely matching the shape of the medullary canal. Note that the forms A protruding areas (clover, buttonhole, trapezoid, triangle) can increase the pressure by limited contacts.

 Externally, the tubular rod can also receive a thread (4k, Figure 8), ridges or splines (4m Figures 10 and 12) or micro-asperities knurling type.

deposition of particles of particles ...

 The advantages are apparent from the description, it is still emphasized flexibility, lightness, self-locking effi cache, elastic modulus variations, expansions on demand, osteogenesis, obtained with a slotted tubular rod and properly arranged .

Claims (1)

 REVENDIC4TIONS  An anchoring rod in a medullary canal for various joint prostheses, characterized in that it has a longitudinal opening (4e) conferring on it a generally tubular shape from its upper end of connection to the body. articulation support up to its free lower end, said rod having good elasticity characteristics. -2- anchor rod according to claim 1 characterized in that the elasticity is given by a longitudinal slit elas ticity (4+). -3- anchor rod according to claim 1, characterized in that the elasticity is given by a biocompatible material. -4- Anchor rod according to claim 2, characterized in that the longitudinal elastic slot (4f) is limited in length. An anchoring rod according to claim 2, characterized in that it is established with external dimensions in section slightly greater than the inner dimensions of the medullary canal; said rod being introduced by forced fitting. -6- Anchor rod according to claim 2, characterized in that it is established with external dimensions in section slightly smaller than the inner dimensions of the nedullary canal, for y introduced freely; the radial expansion with contact pressure for firm anchoring in said channel being obtained by an independent spacer means, within the limits of the elastic deformation of the material. -7- Anchor rod according to claim 6, characterized in that the spacer means is a member (5), preferably of polygonal section and A wedge effect, which is forcedly engaged directly in the longitudinal opening ( 4e).  -8- Anchor rod according to claim 6, characterized in that the spacer means is a member (6), preferably of polygonal section and A wedge effect, which is forcibly engaged between two grooves (49) formed on each side of the longitudinal elastic slot (4f). An anchoring rod according to claim 2, characterized in that it is established with external dimensions in section slightly greater than the inner dimensions of the medullary canal; said rod being narrowed and provided with retaining means in the narrowed position for its free introduction into the medullary canal; the radial expansion with contact pressure for anchoring in said channel being obtained by removing said holding means. -10- Anchor rod according to claim 9, characterized in that the retaining means in the narrowed position of the rod is a member (7> of the clip type, clip, clamp cooperating with projecting shapes (4h) made internally on either side of the longitudinal slot (4fez -11- anchor rod according to claim 2, characterized in that it has in its length one or more trans veruln slots 4i> opening into the longitudinal slot (4f> to ensure differentiated elastic defenders. -12- anchor rod according to any one of claims 1 and 2 characterized in that the longitudinal opening <4e) and the periphery have identical cross-sectional shapes with a wall of reduced thickness and uniform. -13- anchor rod according to any one of claims 1 and 2 characterized in that the longitudinal opening (4e) and the periphery have different sectional shapes. -14- anchor rod according to any one of claims 1 and 2, characterized in that the longitudinal opening (4e) has a sectional shape in evolution in length. -15- Anchor rod according to any one of claims 1 and 2, characterized in that its periphery is equipped directly or reported with means for reinforcing the thread type anchoring (4k), grooves, grooves ( 4m>, microaspérités ...  Rod anchor rod according to any one of claims I and 2, characterized in that all or part of its peripheral surface are made of multiple orifices (4j) for osteogenesis between a filler material stimulating bone growth and bone tissue. -17- anchor rod according to claim 2, characterized in that it is made of biocompatible material having the phenomenon according to the shape memory method, allowing its free introduction into the medullary canal and its radial expansion in contact pressure by temperature difference.